Photosensitive compositions containing microgels

ABSTRACT

A solid photopolymerizable composition, contains addition polymerizable ethylenically unsaturated monomer, initiating system, polymer binder and a microgel wherein preferably the binder and microgel form substantially a single phase and have a similar glass transition temperature above 25° C. Although less preferred the solid composition can function without the binder. A preferred use is as a photoresist.

BACKGROUND OF THE INVENTION

The present invention relates to photosensitive compositions whichcontain an additive component to influence one or more physical and/orchemical properties of the composition. Such properties can include,without limitation, storage stability, photospeed, ability to laminateand adhere to a substrate and ability to laminate over voids in asubstrate. The additive can be added in a concentration to replace aportion or all of a component of the photosensitive composition, e.g.,replacement of binder.

Photosensitive compositions particularly useful as photoresists are wellknown in the prior art. Conventionally these compositions are stored inroll form. The composition is adhered to a support film to form a twoply material such as disclosed in U.S. Pat. No. 4,293,635 or moreconventionally in a three ply material such as U.S. Pat. No. 3,469,982with the composition sandwiched between a support film and a coversheet. The material is unwound from a roll and the cover sheet, ifpresent, is removed from contact with the photosensitive compositionprior to use in lamination to a substrate, e.g., in manufacture ofprinted circuit boards. In storage of the material a potential defect ofcold flow exists. An excessive amount of cold flow results in thematerial becoming unacceptable, e.g., edge fusion occurs which preventsunwinding of a roll without damaging the continuity of thephotopolymerizable composition.

Generally storability with minimization of cold flow is imparted byproper selection and formulation of the components of thephotopolymerizable material. An exception to a need to formulate storagestability in a composition is disclosed in U.S. Pat. No. 3,867,153. Thispublication teaches hardening of the edges of the roll such as byexposure to actinic radiation which prevents cold flow with thephotopolymerizable composition effectively sealed within the roll.

Use of an additive component to change physical properties in acomposition is well known. One example is using beads as a filler in anorganic polymer composition which may be optionally polymerizable asdisclosed in U.S. Pat. No. 4,414,278. The polymeric beads are discrete,substantially nonswellable and crosslinked with an average diameter inthe range of 0.7 to 20 μm.

In contrast to the use of the highly crosslinked nonswellable beads in acomposition are swellable microgels which are a separate and distinctcomponent. Microgel is a term originated in the paint industry and itincludes crosslinked spherical polymer molecules of high molecularweight such as of the order of 10⁹ to 10¹⁰ with a particle size of 0.05to 1 micron in diameter prepared by emulsion polymerization.Crosslinking renders these microgels insoluble but capable of swellingin strong solvent without destroying the crosslinked structure. Thepreparation and use of such microgels is described, e.g., in BritishPat. No. 967,051 and U.S. Pat. No. 3,895,082.

Use of a component described as a microgel in one type of photosensitivecomposition is disclosed in Japanese patent application No. 52,116301.The composition contains a major ingredient of a methacrylate ester anda microgel, a polymerizable monomer, a photoinitiator and athermopolymerization inhibitor. The microgel is a rubber type substanceobtained by a graft polymerization of a vinyl monomer with a so-calledrubber type base material having particle diameter of 0.01 to 10microns. This photosensitive composition is used for offset printing.

A delustering coating composition which contains fine particles isdisclosed in U.S. Pat. No. 4,518,472. The composition is applied to amolded article to provide high abrasion resistance or scratchresistance. Such composition for coating is a liquid which differs fromthe solid films of the present invention.

SUMMARY OF THE INVENTION

The present invention is directed to a photosensitive compositioncomprising

(a) addition polymerizable ethylenically unsaturated monomer,

(b) initiating system activated by actinic radiation,

(c) preformed macromolecular polymer binder, and

(d) microgel,

wherein the photosensitive composition is a solid and wherein at leastone of the following is present:

(i) the polymer binder and microgel form substantially one phase asviewed by the naked eye, or

(ii) the polymer binder and microgel have glass transition temperatureswhich do not differ by more than 50° C. with the microgel having a glasstransition temperature above 25° C.

Although less preferred it is possible to formulate the photosensitivecomposition without the polymeric binder.

DETAILED DESCRIPTION OF THE INVENTION

The starting materials for the solid photosensitive composition of thepresent invention ordinarily present as a film on a flexible backingmaterial are well known in the prior art with the exception of themicrogel of the type disclosed herein. The microgel allows areformulation of the photosensitive composition which can be simply adifferent concentration of components to obtain comparable physicalproperties or comparable processing characteristics particularly in apreferred use as a photoresist in making of a printed circuit board.Alternatively the use of microgels in the photosensitive composition canaid to obtain superior photosensitive formulations, e.g., an increase inphotospeed, better strippability of the composition from a substrate orimproved ability to cover holes in a substrate during processing.

The photosensitive composition will contain the microgel together withone or more addition polymerizable ethylenically unsaturated monomers,and an initiating system activated by actinic radiation and a performedmonomolecular polymer binder. It has been found that a microgel can beused to replace all of the binder components for a composition useful asa photoresist. However in one mode a binder or combination of binders ispresent but in an amount insufficient to obtain all properties necessaryin a commercially acceptable resist. Illustratively a suitablecomposition can be formulated which will not be storage stable withoutthe added microgel component. A microgel can be utilized in a variety ofways to allow reformulation of the photosensitive composition.

For the property of storage stability it can be measured in a short termtest since true storage stability (such as the composition formed into asheet and wound into a roll on a backing sheet) can take a considerableperiod of time, i.e., the order of months or even a year. Thecorrelation of storage stability and particularly lack of substantialcold flow of the photosensitive composition causing edge fusion with ashort term test can be measured herein by creep viscosity test. Astorage stable composition will have a creep viscosity of at least 20megapoise, preferably at least 30 megapoise, and most preferably atleast 40 megapoise. Another test for storage stability would be to storethe composition in roll form for six (6) months at 25° C. or for one (1)month at 40° C.

The introduction of the microgel can also influence photospeed andhigher photospeeds have been obtained with the introduction of themicrogel compared to a similar composition without the microgel.Therefore in one of the suitable modes of the present invention themicrogel is added to facilitate an increase in photospeed.

It has been discovered that the incorporation of microgels in a solidphotosensitive composition as replacement for some or all of a binderprovides thixotropic behavior, where under low shear conditions such asexperienced in a roll during storage the film has high viscosity, butunder high shear conditions such as lamination the photosensitivecomposition present as a dry film flows easily and conforms well to asubstrate copper surface. This property aids in application of thephotosensitive composition to a surface. Illustratively for aphotoresist laminated to a surface such as a copper panel havingpredrilled holes, the ability of the composition to be laminated overthe holes is essential. Microgels allow formulation of compositions withan enhanced ability to resist rupture. This ability is commonly referredto as tenting, where addition of the microgel can be advantageous.

In compositions with a binder employed, the relationships between thebinder and the microgel allows formulations to obtain the beneficialproperties of the present invention, e.g., in a photoresist. One mannerof defining this combination of components is that the polymer binderand microgel will form a single homogeneous phase. This homogeneousphase can be viewed with the naked eye. However, more preferably thepresence of the single phase is present is viewed under a magnificationof 10 times and more preferably a magnification of 100 times.

An alternate manner of describing the combination of a preformedmacromolecular binder and microgel is through glass transitiontemperature. Generally the glass transition temperature will not differby more than 50° C. and more preferably by more than 25° C. Since onepurpose of including the microgel in the composition is to increaseviscosity, the glass transition temperature should also be above roomtemperature (25° C.). Often the binder and microgel will be formulatedfrom common monomers which aids compatibility of the two componentsalthough formulation in this manner is not necessary.

It is understood that the definition of microgel herein is employed inits conventional definition. Such definition of a microgel excludes ahighly crosslinked material such as in U.S. Pat. No. 4,414,278 whichdiscloses beads which are substantially non-swellable. Illustratively aSwelling Test is set forth in this patent on column 4, lines 30 to 45with a statement that any degree of swelling is undesirable. Arepresentative sample of a microgel used in the present inventionfloated in a test solution of the patent rather than sank in accordancewith polymeric beads of this patent. Accordingly this test is notconsidered relevant. Since the degree of crosslinking is controlled inmanufacture of a microgel, a substantially nonswellable crosslinkedpolymeric bead (even of proper size) is not a microgel. Generally themicrogels will be present in an average particle size range of from 0.1to 1 microns and more preferably 0.05 to 0.15 microns.

Preferably the microgels of the present invention will swell in at leastone of the following solvents: n-heptane, carbon tetrachloride, toluene,methylene chloride, ethyl acetate, acetone, acetonitrile, acetic acid,dimethylsulfoxide, dimethylformamide, formamide, water, aqueous ammoniumhydroxide solution containing up to 10% by weight ammonia, aqueouspotassium hydroxide solution containing up to 10% by weight potassiumhydroxide, methylene chloride-methanol solution containing by weight 92%methylene chloride and 8% methanol, aqueous sodium carbonate solutioncontaining by weight 1% sodium carbonate.

The above list of solvent is not represented as being exhaustive of asolvent which will cause swelling of the microgel. However such list isbelieved to qualify microgels with a proper degree of crosslinking.

As a test of swellability a 10 gram sample of the material, i.e., themicrogel, is added to 100 grams of solvent. The microgel will swell atleast 10%, i.e., at least a 10% increase in volume of the microgel willbe obtained. The swelling conventionally will be greater, i.e., at leasta 50% increase. Swelling increases of at least 100% can also be realizedwith many of the microgels.

Since microgels for addition to the photosensitive compositions willgreatly increase the viscosity of a solvent by swelling throughabsorption of solvent, an alternate test is through measurement of anincrease in viscosity of the solvent. Initially the solution viscosityof the solvent is measured such as using a Brookfield viscometer with aspindle appropriate for the viscosity of the solvent. Ten grams of amaterial for testing, i.e. the microgel candidate, is introduced intoone hundred grams of the test solution. The material for testing andsolvent are stirred at room temperature (i.e., approximately 25° C.) fortwenty-four hours. At the end of the time period additional test liquidis added to obtain a final weight of 110 grams, i.e., 100 grams solventand 10 grams of the material for testing. The viscosity is againmeasured using the Brookfield viscometer and a spindle appropriate forthe viscosity of the mixture.

For qualification of a microgel in this procedure, the increase inviscosity of the solvent with the added material will be at least 100centipoise. Preferably the increase will be 1,000 centipoise and morepreferably 3,000 centipoise.

The microgels employed herein differ from introduction of additives inphotosensitive compositions of the prior art. Illustratively themicrogels differ over materials disclosed in Japanese patent applicationNo. 52,116301 which is believed to employ a principle of rubbertoughening through the incorporation of microgels. The mechanism ofrubber toughening of plastics is discussed by Seymour Newman and C. B.Bucknall in "Polymer Blends", D. R. Paul, ed., New York 1978, volume 2,pp. 63-127. The presence of small rubber particles dispersed in a matrixof a more brittle polymer promotes crazing in the matrix polymer onimpact, delaying the onset of crack formation. The dispersed phase mustbe incompatible with the matrix polymer to remain as a discrete phase,and the temperature of use must be above the rubber's glass transitiontemperature in order for it to function as a toughening agent. Both ofthese requirements are met in the Japanese application No. 52-116301.The microgel materials cited (for example, polybutyl acrylate,polybutadiene, styrene/butadiene copolymer rubber, ethylene/propylenecopolymer elastomer, polyisoprene) are referred to as elastomers whichby definition have glass transition temperatures below room temperature.The discussion of the particle size of the rubber material indicatesthat the rubber exists as discrete particles in the finished article.

As previously discussed the filler additives disclosed in U.S. Pat. No.4,414,278 differ from the microgel disclosed since the fillers are notmicrogels. The compositions of U.S. Pat. No. 4,518,472 differ from thecomposition herein since the compositions of the patent are coatingliquids while the present formulations are solids with differentutility.

The microgels of the present invention are conventionally prepared byemulsion polymerization. The microgels are generally formed from 90 to99.5% by weight polymer component and 10 to 0.5% by weight crosslinkingagent with these materials compatible in formation of a continuous phasesystem. The polymer components can be varied during polymerization toproduce core and shell microgel with different interior and exteriorcomposition. In the case where a polymeric binder is employed the weightratio of the microgel to binder can vary widely, e.g., from 1:20 to 1:1.

The microgels can be made from a wide variety of starting materials.Conventionally monoethylenically unsaturated monomers are used inpreparing the bulk portion of the microgel, whereas the crosslinkingagents contain at least two double bonds.

Preferred monomers are methyl methacrylate, ethyl acrylate, methacrylicacid, butyl methacrylate, ethyl methacrylate, glycidyl methacrylate,styrene and allyl methacrylate; while other useful monomers includeacrylonitrile, methacrylonitrile, acrylic acid, methacrylic acid and2-ethyl-hexyl acrylate.

A preferred crosslinking agent is butanediol diacrylate; while othersinclude ethylene glycol dimethacrylate, tetramethylene glycoldiacrylate, trimethylol propane triacrylate, tetraethylene glycoldimethacrylate, methylene bisacrylamide, methylene bismethacrylamide,divinyl benzene, vinyl methacrylate, vinyl crotonate, vinyl acrylate,vinyl acetylene, trivinyl benzene, glycerine trimethacrylate,pentaerythritol tetramethacrylate, triallyl cyanurate, divinylacetylene, divinyl ethane, divinyl sulfide, divinyl sulfone, hexatriene,triethylene glycol dimethacrylate, diallyl cyanamide, glycol diacrylate,ethylene glycol divinyl ether, diallylphthalate, divinyl dimethylsilane, glycerol trivinyl ether and the like.

Conventionally one or more monomers and crosslinking agents aredispersed in water with suitable emulsifiers and initiators inmanufacture of the microgel. Conventional anionic, cationic or nonionicemulsifiers and water soluble initiators can be employed. Examples ofemulsifying agents are sodium lauryl sulfate, lauryl pyridine chloride,polyoxyethylene, polyoxypropylene, colloidal silica, anionic organicphosphates, magnesium montmorillonite, the reaction product of 12 to 13moles of ethylene oxide with 1 mole of octyl phenol, secondary sodiumalkyl sulfates and mixtures thereof. Usually from 0.25 to 4% ofemulsifier based on the total weight of reactants is used. Examples ofinitiators are potassium persulfate, sodium persulfate, ammoniumpersulfate, tertiary butyl hydroperoxide, hydrogen peroxide, azobis(isobutyronitrile), azo bis(isobutyroimidine hydro chloride), variousredox (reduction-oxidation) systems such as hydrogen peroxide andferrous sulfate and well-known persulfate-bisulfate combinations.Usually, from 0.05 to 5% by weight of initiator based on the weight ofcoploymerizable monomers is used.

Microgels suitable for the practice of the present invention can beproduced by the technique of emulsion polymerization as described inU.S. Pat. No. 3,895,082 (Also British Pat. No. 967,051 teaches asuitable method). This technique can also be modified be beginning thereaction with one set of monomers and then varying the ratios for thefinal part of the reaction in order to produce spherical microgels inwhich the first part of the polymer, i.e., the core is different monomercomposition than the outer part of the polymer, i.e., the shell. A widerange of both homopolymer microgels and core shell microgels can beproduced with varying polymer composition and crosslinking. For thepresent invention, it is desired that the glass transition temperatureof the shell not differ from the polymer binder by more than 50° C. andthat the glass transition temperatures of both are and shall be above25° C.

The art of emulsion polymerization is well known concerning reactionconditions to produce spherical microgels dispersed in a water phase.Unless the dispersion can be used as made and contain no objectionalimpurities or byproducts, it is usually necessary to convert themicrogels to a dry powder prior to their use in a photosensitivecomposition. Well-known techniques of coagulation, filtration, washingand drying may be employed for this purpose. Spray drying is aparticularly useful method for the present invention. Generally theamount of crosslinking agent in the microgel will be less than 20% byweight of the overall weight of the microgel and generally less than 10%by weight. It is understood that all of the crosslinking agent need notfunction in crosslinking.

The solubility of the binder or insolubility of the microgels isdetermined by actual test. A sample of the solid material is weighed andplaced in 100 times by weight of solvent (see particularly the solventspreviously listed). The sample is stirred for 15 minutes. Any solidremaining is then removed and dried and finally weighed to determineundissolved solid in comparison to the original sample weight. Becausepolymeric materials are not absolutely uniform and can contain certainimpurities, the material can be considered soluble if up to 10% of theoriginal sample remained undissolved after the test. Conversely thematerial can be considered to be insoluble if it weighs more than 90% ofwhat it did originally.

Generally the microgel will be present in an amount from 1 to 90 percentby weight of the components of monomer, initiating system, binder andmicrogel and preferably 5 to 40%. A more limited example of such rangeis from 8 to 15%.

An example of the suitable concentrations by weight in a photosensitivecomposition based on these constituents is:

(a) from 5% to 50% of an addition polymerizable ethylenicallyunsaturated monomer

(b) from 0.01% to 15% of an initiating system activated by actinicradiation

(c) from 0% to 90% of a preferred macromolecular polymer binder and

(d) from 1 to 90% by weight of a microgel.

A more limited example of component (a) is from 20% to 35% by weight, ofcomponent (b) is from 2% to 10% and of component (c) is 40 to 65%.

Compositions of some of the microgels produced and tested and founduseful for the practice of the present invention are detailed in TableI. All parts are by weight.

                                      TABLE I                                     __________________________________________________________________________    MICROGEL COMPOSITION                                                          MICROGEL                                                                             MMA EA MAA BMA EMA GMA STY                                                                              AMA BDDA                                     __________________________________________________________________________    A      51  29 20  --  --  --  -- 0.5 2                                        B      51  29 20  --  --  --  -- --  2                                        C      51  29 20  --  --  --  -- --  0.5                                      D      51  29 20  --  --  --  -- --  5                                        E      51  29 20  --  --  --  -- --  10                                       F      45  26 29  --  --  --  -- --  2                                        G      51  29 20  --  --  --  -- --  1.0                                      H      51  29 20  --  --  --  -- --  1.5                                      I      51  29 20  --  --  --  -- --  0.75                                     J      51  29 --  --  --  20  -- --  0.75                                     K      43.2                                                                              -- --  31  --  --  20 2.9 2.9                                      L      49.5                                                                              -- --  --  49.5                                                                              --  -- 0.5 0.5                                      M      51  29 20  --  --  --  -- 0.5 0.5                                      N      39  35 26  --  --  --  -- --  2                                        O CORE 54  17 14  --  --  --  -- --  2                                        O SHELL                                                                              48  26 26  --  --  --  -- --  2                                        P CORE 67  22 11  --  --  --  -- --  2                                        P SHELL                                                                              21  41 38  --  --  --  -- --  2                                        Q      63.2                                                                              -- --  31  --  --  -- 2.9 2.9                                      R      9.8 35.3                                                                             23.5                                                                              --  --  --  29.4                                                                             --  1.9                                      S      4.9 40.2                                                                             23.5                                                                              --  --  --  29.4                                                                             --  1.9                                      T      39  39 20  --  --  --  -- --  2.0                                      U      48.1                                                                              -- --  --  48.1                                                                              --  -- 1.9 1.9                                      __________________________________________________________________________     MMA = Methylmethacrylate                                                      EA = Ethyl Acrylate                                                           MMA = Methacrylic Acid                                                        BMA = Butyl Methacrylate                                                      EMA = Ethyl Methacrylate                                                      GMA = Glycidyl Methacrylate                                                   STY = Styrene                                                                 AMA = Allyl Methacrylate                                                      BDDA = Butanediol Diacrylate                                             

As previously discussed the preferred photosensitive formulation withthe microgel will contain a preformed polymeric binder ordinarilypresent in a concentration of not less than 40% by weight based on thecombination of monomer, initiating system, microgel and binder. Suitablebinders which can be used alone, if employed, or in combination with oneanother include the following: polyacrylate and alpha-alkyl polyacrylateesters, e.g., polymethyl methacrylate and polyethyl methacrylate;polyvinyl esters, e.g., polyvinyl acetate, polyvinyl acetate/acrylate,polyvinyl acetate/methacrylate and hydrolyzed polyvinyl acetate;ethylene/vinyl acetate copolymers; polystyrene polymers and copolymers,e.g., with maleic anhydride and esters; vinylidene chloride copolymers,e.g., vinylidene chloride/acrylonitrile; vinylidenechloride/methacrylate and vinylidene chloride/vinyl acetate copolymers;polyvinyl chloride and copolymers, e.g., polyvinyl chloride/acetate;saturated and unsaturated polyurethanes; synthetic rubbers, e.g.,butadiene/acrylonitrile, acrylonitrile/butadiene/styrene,methacrylate/acrylonitrile/butadiene/styrene copolymers,2-chlorobutadiene-1,3 polymers, chlorinated rubber, andstyrene/butadiene/styrene, styrene/isoprene/styrene block copolymers;high molecular weight polyethylene oxides of polyglycols having averagemolecular weights from about 4,000 to 1,000,000; epoxides, e.g.,epoxides containing acrylate or methacrylate groups; copolyesters, e.g.,those prepared from the reaction product of a polymethylene glycol ofthe formula HO(CH₂)_(n) OH, where n is a whole number 2 to 10 inclusive,and (1) hexahydroterephthalic, sebacic and terephthalic acids, (2)terephthalic, isophthalic and sebacic acids, (3) terephthalic andsebacic acids, (4) terephthalic and isophthalic acids, and (5) mixturesof copolyesters prepared from said glycols and (i) terephthalic,isophthalic and sebacic acids and (ii) terephthalic, isophthalic,sebacic and adipic acids; nylons or polyamides, e.g., N-methoxymethylpolyhexamethylene adipamide; cellulose esters, e.g., cellulose acetate,cellulose acetate succinate and cellulose acetate butyrate; celluloseethers, e.g., methyl cellulose, ethyl cellulose and benzyl cellulose;polycarbonates; polyvinyl acetal, e.g., polyvinyl butyral, polyvinylformal; polyformaldehydes.

In the case where aqueous development of the photosensitive compositionis desirable the binder should contain sufficient acidic or other groupsto render the composition processible in aqueous developer. Usefulaqueous-processible binders include those disclosed in U.S. Pat. No.3,458,311 and in U.S. Pat. No. 4,273,857. Useful amphoteric polymersinclude interpolymers derived from N-alkylacrylamides ormethacrylamides, acidic film-forming comonomer and an alkyl orhydroxyalkyl acrylate such as those disclosed in U.S. Pat. No.4,293,635. For aqueous development the photosensitive layer will beremoved in portions which are not exposed to radiation but will besubstantially unaffected during development by a liquid such as whollyaqueous solutions containing 2% sodium carbonate by weight.

Suitable monomers which can be used as the sole monomer or incombination with others include the following: t-butyl acrylate,1,5-pentanediol diacrylate, N,N-diethylaminoethyl acrylate, ethyleneglycol diacrylate, 1,4-butanediol diacrylate, diethylene glycoldiacrylate, hexamethylene glycol diacrylate, 1,3-propanediol diacrylate,decamethylene glycol diacrylate, decamethylene glycol dimethacrylate,1,4-cyclohexanediol diacrylate, 2,2-dimethylolpropane diacrylate,glycerol diacrylate, tripropylene glycol diacrylate, glyceroltriacrylate, trimethylolpropane triacrylate, pentaerythritoltriacrylate, polyoxyethylated trimethylolpropane triacrylate andtrimethacrylate and similar compounds as disclosed in U.S. Pat. No.3,380,831, 2,2-di(p-hydroxyphenyl)-propane diacrylate, pentaerythritoltetraacrylate, 2,2-di(p-hydroxyphenyl)-propane dimethacrylate,triethylene glycol diacrylate,polyoxyethyl-2,2-di-(p-hydroxyphenyl)-propane dimethacrylate,di-(3-methacryloxy-2-hydroxypropyl) ether of bisphenol-A,di-(2-methacryloxyethyl) ether of bisphenol-A,di-(3-acryloxy-2-hydroxypropyl) ether of bisphenol-A,di-(2-acryloxyethyl) ether of bisphenol-A,di-(3-methacryloxy-2-hydroxypropyl) ether of tetrachloro-bisphenol-A,di-(2-methacryloxyethyl) ether of tetrachloro-bisphenol-A,di-(3-methacryloxy-2-hydroxypropyl) ether of tetrabromo-bisphenol-A,di-(2-methacryloxyethyl) ether of tetrabromo-bisphenol-A,di-(3-methacryloxy-2-hydroxypropyl) ether of 1,4-butanediol,di-(3-methacryloxy-2-hydroxypropyl) ether of diphenolic acid,triethylene glycol dimethacrylate, polyoxypropyltrimethylol propanetriacrylate (462), ethylene glycol dimethacrylate, butylene glycoldimethacrylate, 1,3-propanediol dimethacrylate, 1,2,4-butanetrioltrimethacrylate, 2,2,4-trimethyl-1,3-pentanediol dimethacrylate,pentaerythritol trimethacrylate, 1-phenyl ethylene-1,2-dimethacrylate,pentaerythritol tetramethacrylate, trimethylol propane trimethacrylate,1,5-pentanediol dimethacrylate, diallyl fumarate, styrene,1,4-benzenediol dimethacrylate, 1,4-diisopropenyl benzene, and1,3,5-triisopropenyl benzene.

A class of monomers are an alkylene or a polyalkylene glycol diacrylateprepared from an alkylene glycol of 2 to 15 carbons or a polyalkyleneether glycol of 1 to 10 ether linkages, and those disclosed in U.S. Pat.No. 2,927,022, e.g., those having a plurality of addition polymerizableethylenic linkages particularly when present as terminal linkages.Especially preferred are those wherein at least one and preferably mostof such linkages are conjugated with a double bonded carbon, includingcarbon double bonded to carbon and to such heteroatoms as nitrogen,oxygen and sulfur. Outstanding are such materials wherein theethylenically unsaturated groups, especially the vinylidene groups, areconjugated with ester or amide structures.

Preferred free radical-generating addition polymerization initiatorsactivatable by actinic light and thermally inactive at and below 185° C.include the substituted or unsubstituted polynuclear quinones which arecompounds having two intracyclic carbon atoms in a conjugatedcarbocyclic ring system, e.g., 9,10-anthraquinone,1-chloroanthraquinone, 2-chloroanthraquinone, 2-methylanthraquinone,2-ethylanthraquinone, 2-tert-butylanthraquinone,octamethylanthraquinone, 1,4-naphthoquinone, 9,10-phenanthrenequinone,1,2-benzanthraquinone, 2,3-benzanthraquinone,2-methyl-1,4-naphthoquinone, 2,3-dichloronaphthoquinone,1,4-dimethylanthraquinone, 2,3-dimethylanthraquinone,2-phenylanthraquinone, 2-3-diphenylanthraquinone, sodium salt ofanthraquinone alpha-sulfonic acid, 3-chloro-2-methylanthraquinone,retenequinone, 7,8,9,10-tetrahydronaphthacenequinone, and1,2,3,4-tetrahydrobenz(a)anthracene-7,12-dione. Other photoinitiatorswhich are also useful, even though some may be thermally active attemperatures as low as 85° C., are described in U.S. Pat. No. 2,760,863and include vicinal ketaldonyl alcohols, such as benzoin, pivaloin,acyloin ethers, e.g., benzoin methyl and ethyl ethers;α-hydrocarbon-substituted aromatic acyloins, including α-methylbenzoin,α-allylbenzoin and α-phenylbenzoin. Photoreducible dyes and reducingagents disclosed in U.S. Pat. Nos.: 2,850,445; 2,875,047; 3,097,096;3,074,974; 3,097,097; and 3,145,104 as well as dyes of the phenazine,oxazine, and quinone classes; Michler's ketone, benzophenone,2,4,5-triphenyl-imidazolyl dimers with hydrogen donors, and mixturesthereof as described in U.S. Pat. Nos.: 3,427,161; 3,479,185; and3,549,367 can be used as initiators. Similarly the cyclohexadienonecompounds of U.S. Pat. No. 4,341,860 are useful as initiators. Alsouseful with photoinitiators and photoinhibitors are sensitizersdisclosed in U.S. Pat. No. 4,162,162.

Thermal polymerization inhibitors that can be used in photopolymerizablecompositions are: p-methoxyphenol, hydroquinone, and alkyl andaryl-substituted hydroquinones and quinones, tert-butyl catechol,pyrogallol, copper resinate, naphthylamines, beta-naphthol, cuprouschloride, 2,6-di-tert-butyl-p-cresol, phenothiazine, pyridine,nitrobenzene and dinitrobenzene, p-toluquinone and chloranil. Alsouseful for thermal polymerization inhibitors are the nitrosocompositions disclosed in U.S. Pat. No. 4,168,982.

Various dyes and pigments may be added to increase the visibility of theresist image. Any colorant used, however, should preferably betransparent to the actinic radiation used.

In use the photosensitive composition for application to a substratesuch as in making a printed circuit board, is conventionally supplied bya film which is well known in the art.

A suitable support preferably having a high degree of dimensionalstability to temperature changes may be chosen from a wide variety offilms composed of high polymers, e.g., polyamides, polyolefins,polyesters, vinyl polymers, and cellulose esters. A preferred supportfor the present invention is polyethylene terephthalate. Also generallya cover sheet is present in the appropriate side of the photosensitivecomposition present in film form. The protective cover sheet is removedprior to lamination of the photosensitive composition to a substrate.The cover sheet may be chosen from the same group of polymer filmslisted as supports. Polyethylene and polyethylene terephthalate areparticularly useful.

Although in the above disclosure the photosensitive compositions havebeen disclosed as containing a polymeric binder, it is understood thesuitable compositions which can function for example as photoresistsneed not contain a binder. In such case the photosensitive compositionneed only contain (1) an addition polymerizable ethylenicallyunsaturated monomer, (2) an initiating system activated by actinicradiation and (3) a microgel. Generally the percentage of thesecomponents on the basis of these three constituents will be by weight10% to 60% and preferably 15% to 35% for component (1); 0.01% to 15% andpreferably 2% to 10% for component (2) and 25% to 90% and preferably 30%to 65% for component (3). It is understood that in such compositions, apreformed polymer binder will not be present but conventional additivescan be added such as those previously mentioned.

A preferred use of compositions characterized herein is as a photoresistor a solder mask such as in making a printed circuit board. Suchtechniques are conventional in the art employing a solid material, e.g.U.S. Pat. No. 3,469,982. The process is directed to laminating aphotosensitive or a substrate comprising:

(a) laminating to the substrate a supported solid photosensitive film,

(b) imagewise exposing the layer to actinic radiation.

(c) removing unexposed areas of the layer to form resist areas,

(d) permanently modifying areas of the substrate which are unprotectedby the resist areas by etching the substrate or by depositing a materialonto the substrate.

The support is conventionally removed before or after the exposure step.In the case of solder mask utility the step of depositing a material canbe by application of solder. In a utility not involving direct use as asolder mask in initial application to a substrate (which is conductivewith copper preferred circuitry therein) the resist areas are removedafter step (d) which is conventional.

The following examples serve to illustrate, the practice of the presentinvention. All percentages, ratios and parts are by weight unlessotherwise indicated.

EXAMPLE 1

Preparation of Microgel A Table I composition; 51 methylmethacrylate, 29ethyl acrylate, 20 methacrylic acid, 2 allylmethacrylate and 2butanedioldiacrylate crosslinker.

The emulsion polymerization apparatus consisted of a 5 liter, 4 neckedflask equipped with a mechanical stirrer, 1 liter addition funnel,thermometer, nitrogen inlet, water cooled condenser and a heatingmantle. The flask was charged with 3360 g of deionized water and 20 g ofa 30% aqueous solution of sodium lauryl sulfonate and this surfactantsystem was heated to 80° C. under a nitrogen atmosphere. At thattemperature, 25% of a monomer mixture consisting of 420 gmethylmethacrylate, 240 g ethyl acrylate, 165 g methacrylic acid, 16 gallyl methacrylate and 16 g 1,4-butanediol diacrylate, was added in oneshot. This was followed immediately by the addition of 10 ml of a 5%aqueous solution of potassium persulfate and 10 ml of a 7% aqueoussolution of potassium phosphate. The reaction mixture turned milky andexothermed to 85° C. The remainder of the monomer mixture was added overa period of 90 minutes while maintaining the temperature between 80°-88°C. When the addition was finished the reaction mixture was heated for anadditional 2 hours at 80°-85° C. The bluish milky emulsion was cooled toroom temperature and coagulated by adding methanol. The resulting slurrywas filtered, washed twice with water, sucked dry and the resulting finepowder was dried in an oven at 100° C. for four hours. The sphericalshape of the powder particles was verified by microscopic examination.

EXAMPLE 2

Microgels B to N and Q to U in Table I

Microgels were prepared as in Example 1 except that the monomer mixturewas varied to give the the indicated composition.

Core Shell Microgels O and P Table I

Using the apparatus and basic procedure of Example 1, a variation wasmade in which a first monomer mixture reacts to form a core portion anda second monomer mixture completes the balance of the emulsionpolymerization to produce a shell with a different composition. MicrogelO was prepared with a first monomer mixture of 315 g methylmethacrylate,180 g ethyl acrylate, 55 g methacrylic acid and 10.7 g 1,4 butanedioldiacrylate, which was added over 50 minutes. Then a second monomermixture of 105 g methylmethacrylate, 60 g ethyl acrylate, 110 gmethacrylic acid and 5.3 g 1,4 butanediol diacrylate was added over 40minutes.

Microgel P was similarly prepared by altering the monomer mixtures.

EXAMPLE 3

Comparative photoresist coating compositions were prepared as follows:

    ______________________________________                                        Additive             Control  Invention                                       ______________________________________                                        Polymer binder methyl-                                                                             62.5     52.5                                            methacrylate/ethylacrylate/                                                   methacrylic acid 51/29/20                                                     mol. wt. 50,000 acid no. 130                                                  Tg 87° C.                                                              Microgel B           --       10.0                                            Polyox ® WSRN-3000 polyethylene                                                                0.5      0.5                                             oxide mol. wt. 400,000                                                        Ethoxylated trimethylolpropane                                                                     23.0     23.0                                            triacrylate monomer                                                           Itaconic acid        1.0      1.0                                             Maleic acid          1.0      1.0                                             Urethane diacrylate monomer                                                                        4.0      4.0                                             Ethyl paradimethylaminobenzoate                                                                    2.0      2.0                                             Michler's ketone     0.15     0.15                                            Benzophenone         5.2      5.2                                             4-methyl-4-trichloromethyl-                                                                        0.1      0.1                                             cyclohexadienone                                                              Leuco crystal violet 0.3      0.3                                             Diethyl hydroxylamine                                                                              0.2      0.2                                             Victoria green C.I. #42000                                                                         0.04     0.04                                            Victoria blue C.I. #42575                                                                          0.04     0.04                                            ______________________________________                                    

The composition was dissolved for coating in 67% by weight of solventcomprising 93% methylene chloride and 7% methanol. Films ofapproximately 1.5 mil thickness were produced after coating on a supportand drying to remove the solvent.

Film samples were laminated to copper and tested for standardphotoresist properties of photospeed, resolution, development in 1%aqueous sodium carbonate and stripping in 1.5% aqueous potassiumhydroxide. In addition samples were tested for creep viscosity using theprocedures originated by Diens and Klemm published in the Journal ofApplied Physics, Vol. 17 pages 458 to 471, 1946 on a Du Pont ThermalMechanical Analyzer attached to a 1090 console. Compared to the controlthe invention had slightly longer development and stripping strippingtimes at equivalent resolution but the photospeed was a full ⁶ √2 stephigher. The control had a creep viscosity of 34 megapoise whereas theincorporation of microgels increased the value to 43 megapoise.

The flexibility and adhesion of the photoresist compositions to copperwas tested on both freshly laminated and aged laminated samples. Boththe control and the invention were comparable when the copper was bentto varying angles or a crosshatched pattern scratched into thephotoresist with a knife was covered with transparent adhesive tape andpulled off. Samples of both films were able to withstand the same amountof bending before showing surface fracture and with the same amount ofcrosshatching a similar amount of photoresist was removed by the tape.

Both films were tested for tenting, i.e., the ability of a film tomaintain its integrity when coated over a void. Cleaned copper-cladpanels had 100 holes each of the following diameters drilled: 6 mm, 4 mmand 3 mm. A photoresist film was then laminated over these holes using aRiston® model HRL-24 hot roll laminator at 105° C.. The laminated panelwas irradiated coventionally with a high pressure mercury vapor lamp tophotopolymerize the layer over the holes. The coversheet was removed andthe film was developed by lightly spraying with a 1% aqueous sodiumcarbonate solution and the number of broken tents was measured. Thepanels were then run through an acid etch and with approximately 1N HClat pressures of 30/28 psi and broken tents were again measured. Theresults showed a general improvement in ability to tent as theconcentration of microgel increased.

A further photoresist coating composition was prepared with the samecombination of components as the "Invention" except the ethoxylatedtrimethylolpropane triacrylate monomer was 24.5 (rather than 23.0), theitaconic acid was 0.5 (rather than 1.0), maleic acid was O (rather than1.0) and Victoria blue was 0.02 (rather than 0.04). Improved resultswere obtained over the control and the composition labelled "Invention".

EXAMPLE 4

Photoresist compositions were prepared as in Example 3 except thatdifferent levels of binder replacement were used up to and includingtotal replacement of soluble binder by insoluble microgel. The relativeproperties of the control and microgel films are shown below.

    ______________________________________                                        Variation of Microgel Content                                                 ______________________________________                                        % Microgel                                                                              0     10     12.4 15.6 19    31.2  62.5                             as film solids                                                                % Microgel                                                                              0     16     20   25   30    50    100                              as binder                                                                     replacement                                                                   Dev. Rate                                                                              875    805    788  735  709   551   116                              Photospeed                                                                             22     23     24   24   24-25 23-24  23                              Resolution                                                                             good   good   good good poor  poor  very                                                                          poor                             Time to strip                                                                          28     35     35   36   38    45     75                              Flex/    =      =      =    =    =     =     poorer                           adhesion                                                                      Creep    34     43     58   53   63    163   542                              viscosity                                                                     ______________________________________                                         Development Rate is milligrams per minute removed on a sample which was 9     square inches                                                                 ##STR1##                                                                      Time to strip is in seconds                                                   Creep viscosity is megapoise                                                  = is similar                                                             

While the film containing only microgel as a binder shows severedegradation in resolution and flexibility/adhesion, it still canfunction as a film suitable for making printed wiring boards and wouldbe employed most advantageously where high creep viscosity was animportant factor.

It is also apparent from the data presented that when only 25% or lessof the binder has been replaced by microgel there is a speed and creepviscosity advantage as a tradeoff for decreased development andstripping, but without any sacrifice in important properties such asresolution and flexibility/adhesion.

EXAMPLE 5

Photoresist compositions were prepared as in Example 3 except that themicrogel particles used to replace 10% of the binder had varying levelsof crosslinking. The results below compare the effects of 2%, 5% and 10%crosslinking of the microgels and a control film without microgeladdition. Percent crosslinking denotes parts crosslinking monomer addedduring synthesis. The films prepared were 1.3 mil instead of 1.5 mil inExample 1 in order to provide a more severe test of tenting capability.

    ______________________________________                                        Microgel Crosslinking                                                                   Control                                                                              2%        5%      10%                                        ______________________________________                                        Dev. Rate   814      781       790   838                                      Photospeed  22       23-24     23-24 23                                       Time to strip                                                                             24       28        30    34                                       Creep       52       61        63    112                                      viscosity                                                                     Tenting (6 mm                                                                               2%       7%        9%   15%                                     holes unbroken)                                                               ______________________________________                                         Units are as previously specified                                        

These tests with 1.3 mil films show the consistent improvement intenting, creep viscosity and photospeed for microgel incorporation.

EXAMPLE 6

A control and a coating containing 10% microgels were prepared as inExample 3 but no solvent was added. Instead the compositions weremelt-extruded onto a support to examine relative properties in theabsence of any organic solvent. When samples were laminated to copperand given chemical and physical tests it was determined that with theexception of longer strip times for both the control and the invention,the incorporation of microgels produced an advantage of photospeed andcreep viscosity as a tradeoff lower higher development rate and longertime to strip. When samples were tested with 1.3 mil films as in Example3 a significant advantage in tenting was observed for the inventionversus the control. Thus it can be concluded that the microgel advantageis independent of coating method used for film preparation.

EXAMPLE 7

Photopolymer compositions were prepared similar to Example 3 except thatdifferent microgels were used. Table I contains a summary of themicrogel compositions incorporated in these compositions to producephotoresist films. It was observed that microgels containing acid groupswere easier to incorporate into these coating compositions, i.e.,requiring shorter dispersion times.

EXAMPLE 8

Several photopolymer compositions were prepared as in Example 3 exceptthat different primary binders and monomers were employed with themicrogels. Binders used were: polymer ofmethylmethacrylate/ethylacrylate/acrylic acid/cyclohexylmethacrylate15/40/25/20; amphoteric interpolymer from 40% n-tertoctyl acrylamide,34% methylmethacrylate, 10% acrylic acid, 6% hydroxy propyl methacrylateand 4% t-butyl amino ethyl methacrylate; polymer of styrene butylmaleate; polymer of methyl methacrylate/2-ethyl-hexylacrylate-methacrylic acid 65/31/2 and polymer of styrene methacrylicacid. Other monomers used were trimethylolpropane triacrylate andpentaerythritol triacrylate. Film samples were prepared similar toexample in which the thicknesses varied from 1.29 to 1.79 mil due toviscosity differences. Improved creep viscosity and photospeed wasobserved when microgels were incorporated compared to a control with nomicrogels.

EXAMPLE 9

Microgels B and J from Table I were dispersed into the polymer binder ofExample 3 using a 2-roll mill. Two 100 g portions of 50/50microgel/polymer were each mixed with 100 ml of methylenechloride/methanol 93/7 and allowed to stand for about 1 hour. The tworoll mill was cleaned with 3:1 binder/triethylene-glycoldiacetate. Thematerial was milled for 10 minutes at 175° C. Mixing and melt lookedgood and the material was cut off and reintroduced several times duringthe run. At the end of 10 minutes the melted mixture was cut off themill and allowed to cool. Prior to use in a photopolymer composition thematerial was hand ground. Films prepared with the milled materialsshowed the same creep viscosity advantage as compositions prepared bystirring.

EXAMPLE 10

Film samples with the composition of Example 3 containing microgelsprepared as in Example 1 and melt extruded as in Example 6 were testedfor printed circuit board manufacture. The films were laminated to acopper clad board and exposed on a PC24 Riston® exposure device througha circuit board test pattern. The film cover sheet was removed and theexposed boards were processed in a Riston® Aqueous Development SystemADS-24 with 1% aqueous Na₂ CO₃ at 30° C. at a conveyor setting of 150using a top spray pressure of 30 psi and bottom of 29 psi. The sampleswere etched to remove copper in the nonresist areas and then the resistwas removed by stripping with 1.5% aqueous potassium hydroxide. Adetailed examination of the resulting printed circuit boards showedequivalent quality to boards similarly prepared with commercialphotoresist films.

EXAMPLE 11

The comparative solubility of the binder and insolubility of themicrogels was determined by actual test. A 1 gram sample in 100 ml of 2%aqueous sodium carbonate was stirred at 29° C. for 10 minutes. Thesample was centrifuged for 40-45 minutes and the supernatant decanted.The remaining solid was washed with a minimum amount of water,centrifuged, dried and weighed. The supernatant was also dried andweighed. The following is an experimental comparison of the polymerbinder of Example 1 and microgels C and G of Table I.

    ______________________________________                                        Sample        Solid Remaining Grams                                           ______________________________________                                        Polymer binder                                                                              0.0150                                                          Microgel C    0.9736                                                          Microgel G    0.9674                                                          ______________________________________                                    

EXAMPLE 12

The comparative swellability of the microgel B and the prior artpolytrimethylolpropanetriacrylate beads of Example 1 of U.S. Pat. No.4,414,278 was determined by actual test. The viscosity of a testsolution of 8% by weight methanol and 92% by weight methylene chloridewas determined to be 2.5 centipoise using a Brookfield viscometer with aNo. 2 spindle. 10 g solid material of microgel B andpolytrimethylolpropane triacrylate were introduced into separate 100 gtest solutions and stirred for 24 hours. The weight was brought up to110 g at the end of this time period to correct for any evaporation.Using the same Brookfield viscometer with a No. 2 spindle the viscosityof microgel B solution was 3800 centipoise while the solution ofpolytrimethylolpropane triacrylate beads was 5.0 centipoise. Inappearance at the end of the 24 hour period microgel B in the testsolution was invisible, having assumed the same refractive index as thetest solution (apparently by swelling) while the comparative test beadsin the test solution had an identical milky appearance observed at thetime of their initial introduction in the test solution.

What is claimed is:
 1. A photosensitive composition comprising(a)addition polymerizable ethylenically unsaturated monomer, (b) initiatingsystem activated by actinic radiation, (c) preformed macromolecularpolymer binder, and (d) microgel which swells at least 10% by volume ina solvent selected from the group consisting of n-heptane, carbontetrachloride, toluene, methylene chloride, ethyl acetate, acetone,acetonitrile, acetic acid, dimethylsulfonxide, dimethylformamide,formamide, water, aqueous ammonium hydroxide solution containing up to10% by weight ammonia, aqueous potassium hydroxide solution containingup to 10% by weight potassium hydroxide, methylene chloride-methanolsolution containing by weight 92% methylene chloride and 8% methanol,and aqueous sodium carbonate solution containing by weight 1% sodiumcarbonate,wherein the photosensitive composition is a solid and whereinat least one of the following is present: (i) the polymer binder andmicrogel form substantially one phase as viewed by the naked eye, or(ii) the polymer binder and microgel have glass transition temperatureswhich do not differ by more than 50° C. with the microgel having a glasstransition temperature above 25° C.
 2. The composition of claim 1wherein properties (i) and (ii) are present.
 3. The composition of claim1 wherein the substantially one phase is present and observable after amagnification of 10 times.
 4. The composition of claim 2 wherein thesubstantially one phase is present and observable after a magnificationof 100 times.
 5. The composition of claim 1 wherein the glass transitiontemperature of the polymer binder and the microgel do not differ by morethan 25° C.
 6. The composition of claim 1 wherein the microgel swells atleast 50% in at least one of the solvents.
 7. The composition of claim 1which has a creep viscosity of at least 20 megapoise.
 8. The compositionof claim 7 which has a creep viscosity of at least 40 megapoise.
 9. Anarticle comprising a storage stable photosensitive composition supportedby a flexible film with the article wound in a roll whereby thephotosensitive composition comprises(a) addition polymerizableethylenically unsaturated monomer, (b) initiating system activated byactinic radiation, (c) preformed macromolecular polymer binder, and (d)microgel which swells at least 10% by volume in a solvent selected fromthe group consisting of n-heptane, carbon tetrachloride, toluene,methylene chloride, ethyl acetate, acetone, acetonitrile, acetic acid,dimethylsulfoxide, dimethylformamide, formamide, water, aqueous ammoniumhydroxide solution containing up to 10% by weight ammonia, aqueouspotassium hydroxide, methylene chloride-methanol solution containing byweight 92% methylene chloride and 8% methanol, and aqueous sodiumcarbonate solution containing by weight 1% sodium carbonate,wherein thephotosensitive composition is a solid and wherein at least one of thefollowing is present: (i) the polymer binder and microgel formsubstantially one phase as viewed by the naked eye, or (ii) the polymerbinder and microgel have glass transition temperatures which do notdiffer by more than 50° C. with the microgel having a glass transitiontemperature above 25° C.
 10. The article of claim 9 wherein properties(i) and (ii) are present.
 11. The article of claim 9 wherein thesubstantially one phase is present and observable after a magnificationof 10 times.
 12. The article of claim 11 wherein the substantially onephase is present and observable after a magnification of 100 times. 13.The article of claim 9 wherein the glass transition temperature of thepolymer binder and the microgel do not differ by more than 25° C. 14.The article of claim 1 wherein the microgel swells at least 50% in atleast one of the solvents.
 15. The article of claim 9 which has a creepviscosity of at least 20 megapoise.
 16. The article of claim 15 whichhas a creep viscosity of at least 40 megapoise.